If a player uses a text-changing effect to make a land type be listed as producing two different colors, the player tapping the land for mana can choose to produce mana of either color. But if it produces more than one mana, all mana is of the same color.

4/15/2013

If a land has more than one basic land type, the player tapping the land for mana can choose to produce mana of either color. But if it produces more than one mana, all mana is of the same color.